Power-operated scissor-type tools, such as shears, and electrical cable cutters in particular, commonly have a pair of blades which are relatively displaceable about a common axis formed by a pivot traversing both blades with one blade lying against the other at the pivot so that the cutting edges of the two blades lie in parallel planes and engage a workpiece, such as an electrical cable, with a shearing action. The blades meet and pass at a contact plane common to them both and which ultimately is the plane of the cut through the workpiece.
In order to ensure a clean and straight cut through the workpiece, the cutter blades must be held together with force to resist the tendency of the cutting edges to move out of the aforementioned cutting plane and thereby clamp the workpiece or pieces thereof between the blades, transform the cut into an irregular tear, or both. Furthermore, since the forces applied to the blade lie out of the cutting plane, the blades may be bent, twisted or damaged and the entire device rendered unsuitable.
Consequently, the pressing force holding the blades against one another must be considerable to avoid these disadvantages. However, if this pressing force is excessive, friction between the blades causes them to block and renders the device inoperative.
Hand-held tools of this type, such as shears or scissors, are commonly provided with bolts, screws and the like enabling adjustment of the pressing force. However, such devices are seldom fully satisfactory even for hand tools because frequently the pressing force is insufficient for the cutting of heavy articles or is so great that the tool cannot be readily manipulated.
With conventional power-operated shears, such as electrical cable cutters, the tendency is to increase the pressing force to a maximum which calls for double-acting cylinders so that the necessary opening force can be generated against the friction effect described. This is disadvantageous when, as is the case of many cable cutters, the force-applying means is a foot-operated or hand-operated pump since the latter must be actuated for the opening stroke as well as the closing stroke in a time-consuming series of operations. Furthermore, the use of high pressing forces at all times and both during the opening and closing strokes increases the wear of the blades and requires frequent replacement thereof.